Topic 6 Transport in Plants Flashcards
Why do plants require water?
- Photosynthesis
- Maintenance of structure
- Cooling effect
Why do plants require mineral ions?
For growth e.g nitrates are required to produce proteins
Which structure in plants is adapted for the uptake of water and minerals?
Root hair
How is water transported into root hairs?
- Lower concentration of water in root hair cells than in the soil
How are minerals transported into root hairs?
- Lower concentration of mineral ions in the soil than in the root
- Root hair cells take up mineral ions by active transport
How are plant roots adapted for the absorption of water and minerals?
- Long hairs that extend from the cell body, increasing the surface area for absorption
- Many mitochondria which produce ATP for active transport of mineral ions
Name the two plant transport tissues
Xylem
Phloem
What is the function of the xylem?
Transports water and minerals up the plant, from the roots to the leaves via the transpiration
Describe how the xylem is adapted to its function:
- Composed of dead cells laid end to end to form a long hollow, continuous column
- No end walls which provides little resistance to the passage of water
- Thick cell wall strengthened with lignin to provide support
What is the function of the phloem?
Transports sugars up and down the stem from photosynthetic tissues (e.g mature green leaves) to non-photosynthetic tissues (e.g developing seeds) via translocation
What are the two cell types that make up the phloem?
Sieve tube elements
Companion cells
Describe how the phloem is adapted to its function
- Sieve tube elements: are long, thin cells, laid end to end with perforated end plates to enable the flow of sugars. They have no nucleus and little cytoplasm to allow sugars to flow easily.
- companion cells: contain dense cytoplasm. They provide energy for processes in both cell types.
What is transpiration?
The loss of water vapour from the parts of a plant exposed to the air due to evaporation and diffusion
Where does the majority of transpiration take place?
Leaves
Describe the process of transpiration:
- Water evaporates from the mesophyll cell surfaces and diffuses out of the stomata
- Water molecules are drawn up the xylem vessels to replace the water that has been lost
- This causes more water molecules to be absorbed from the soil into root hair cells.
How does the transpiration stream transport mineral ions?
Mineral ions are dissolved in the water that is carried by the transpiration stream
How does the transpiration stream transport mineral ions?
Mineral ions are dissolved in the water that is carried by the transpiration strea,
What are stomata?
They are pores found in the lower epidermis of a lead which allow gas exchange
What are guard cells?
Specialised cells surrounding stoma that change shape to control the size of the pore
How do guard cells control the size of stomata?
To open the stomata:
Water enters guard cells. They swell and become turgid. The bend and draw away from each other, opening the stomata.
What factors affect the rate of transpiration?
- Light intensity
- Temperature
- Air movement
Describe how light intensity affects the rate of transpiration:
- High light intensity, greater number of stomata open to allow gas exchange for photosynthesis
- Rate of photosynthesis increases so more water is taken up from soil, pushing water up the xylem
- More water vapour diffuses out of the stomata rate of transpiration increases
Describe how low light intensity affects the rate of transpiration:
At a low light intensity, fewer stomata are open so the rate of transpiration decreases
Describe how temperature affects the rate of transpiration:
- Temperature increases, water molecules have more KE so rate of diffusion increases
- Photosynthesis also increases so more water is taken up from the soil, pushing water up the xylem
- More water vapour diffuses out of the stomata rate of transpiration increases
